Method of fabricating a metal tubular heat exchanger having internal passages therein

ABSTRACT

A heat exchanger tube, and a method and apparatus for forming a heat exchanger tube are disclosed. The tube is formed from a metal strip having inflatable passages. The passages are inflated after the tube is formed. In use, one fluid flows through the tube and at least one fluid flows through the wall passages. Another fluid, contacting the exterior of the tube, may be employed.

United States Patent 1191 1111 3,831,246 Morris Aug. 27, 1974 [5 METHODOF FABRICATING A METAL 3,172,194 3/1965 Pauls 29/1573 v 3,173,479 3/1965Hever 165/122 TUBULAR HEAT EXCHANGER HAVING 3,276,108 10/1966 White29/1573 v x INTERNAL PASSAGES THEREIN Jack Morris, Fort Lauderdale, Fla.

Olin Corporation, New Haven, Conn.

F1166; Mar. 22, 1973 Appl. No.2 343,740

lnventor:

Assignee:

US. Cl. 29/ 157.3 V, 29/4709 Int. Cl... B2ld 53/02, B23p 15/26 Field ofSearch 29/ 157.3 V, 421 R, 470.9

References Cited UNITED STATES PATENTS l0/l96l Thomas 29/421 R 10/1961Wilkins 29/1573 V Primary Examiner-Charles W. Lanham AssistantExaminer-O. C. Reiley, Ill

Attorney, Agent, or Firm-Charles E. Sohl; Robert H. Bachman [57]ABSTRACT A heat exchanger tube, and a method and apparatus for forming aheat exchanger tube are disclosed. The tube is formed from a metal striphaving inflatable passages. The passages are inflatedafter the tube isformed. In use, one fluid flows through the tube and at least one fluidflows through the wall passages. Another fluid, contacting the exteriorof the tube, may be employed.

10 Claims, 14 Drawing Figures BACKGROUND OF THE INVENTION Heatexchangers are usually designed so as to exchange heat between twodifferent fluids. Typical examples are the condensation of steam duringthe distillation of water and the cooling of internal combustion enginesby rejection of heat to the atmosphere through the radiator.

This invention relates to a new and improvedtype of heat exchangeelement and the process andapparatus for making and using it wherein theelement consists of a tube having at least one continuous passage in thewall of the tube with the length of the wall passage significantlyexceeding the length of the tube.

SUMMARY OF THE INVENTION In its broadest form'the instant inventioncomprises a tubular heat exchange element having at least one passage inthe tube wall. In operation one fluid flows through the tube and asecond fluid flows through the passage in the tube wall. The passage inthe tube wall is constructed so that it has alength of at least30percent greater than the length of the tube.

In a preferred embodiment the extent of each'wall passage is determinedby a stop weld pattern applied between two strips of metal. The twostrips are then pressure welded together to form a composite metalstrip. The welded strip is formed into tubing, the longitudinal edges ofthe composite strip are welded together to form a tube, and the passagesare formed by an inflation process applied to the unwelded areas of thecomposite strip.

In the normal course of such an inflation process, the resultantpassages will protrude out from both the inner and outer surfaces of thetube. Another embodiment of this invention provides a means forinflation including the application of a differential pressure duringthe inflation process so as to eliminate the protrusion of the passageeither on the inner or outer surface of the tube.

Another embodiment of this invention consists of a tubular elementhaving more than one passage in the tube wall so that more than twofluids may be caused to flow through the wall passages.

Yet another embodiment of this invention encompasses the application ofinternal and/or external fins to the tubular member to improve heattransfer.

It is an object of this invention to provide an improved tubular heatexchange element comprising a tube having at least one continuouspassage in the wall of the tube wherein the length of the passage is atleast 30 percent greater than thelength of the tube.

It is another object of this invention to provide a process for makingthe above noted heat exchange element.

It is another object to provide an element and process as above whereinthe passage or passages in the tube wall are defined by a stop weldpattern.

It is another object to provide an apparatus for the inflation of thepassage or passages so that there is no protrusions from one of eitherthe inner or the outer surfaces of the tube.

It is another object of this invention to provide fins, applied eitherto the inner or outer surface of the tube so as to improve heattransfer.

DESCRIPTION OF THE DRAWINGS FIG. 1A shows a cut away view of the metalstrips used to form the blank of the present invention, prior to thewelding process.

FIG. 1B shows the blank of the present invention after the pressurewelding process.

FIG. 2 shows a tube formed from the blank of FIG. lB prior to theinflation of the wall passage.

FIG. 3 shows the tubing of FIG. 2 after the inflation of .the wallpassages.

FIGS. 4A, 4B and 4C show different embodiments of the stop weld patternin the blank of FIG. 18.

FIG. 5 shows an inflated tubing formed from the blank shown in FIG. 4B.The passages in FIG. 5 have been inflated so that the protrusion of thewall passage has been restricted to the interior of the tube.

FIG. 6 shows the tubing of FIG. 5 with a plurality of radial finsattached to the exterior of the tube.

FIG. 7 shows the apparatus for inflating tubes as shown in FIGS. 5 and6.

FIG. 8 shows a tubing formed from the blank of FIG. 4B but inflated sothat the protrusion of the wall passages occurs on the exterior of thetube.

FIG. 9 shows the tubing of FIG. 8 with a plurality of internal fins forimproved heat transfer.

FIG. 10 shows an apparatus for inflating tube passages as shown in FIGS.8 and 9.

FIG. 11 shows a tubing according to the present invention having a layerof thermal insulation on its exterior surface.

DESCRIPTION OF THE INVENTION The instant invention comprises a new formof annular tubular heat exchange element wherein the tube has at leastone continuous passage in the tube wall. In operation one fluid flowsthrough the tube and a second fluid flows through the passage in thetube wall. The passage in the tube wall is so constructed that is has alength which significantly exceeds the tube length.

Of course, other embodiments are possible. For example, more than onewall passage may exist so that more than two fluids may flow through theheat exchanger. In another embodiment fins may be applied either to theinterior or exterior of the tube so as to improve heattransfer. Theinstant invention also includes means for forming the tube wall passagesso that the tubular heat exchange element has either its interiorsurface or exterior surface smooth and free from the protrusion of thewall passages.

Referring now to the drawings, there is illustrated an exemplary processfor making tubular sheet metal heat exchangers of the type described inthe instant invention. While the concept of having passages in the wallof a heat exchanger tube can be applied to various types of tubemanufacture, for example extrusions, the process to be described hereinpossess the advantage that the length of the wall passage can easily bevaried and can significantly exceed the length of the tube. Because ofthe thin gage of the sheet metal employed, one can obtain better heatexchange performance as compared to the use of an extrusion or similarmaterial.

US. Pat. No. 3,004,330 issued to Wilkins describes a process forproviding a wall passage in a tube. However, the wall passages in thepatent are constrained to be the same length as the tube which reducestheir heat exchange efficiency. Additionally the process described inthe instant invention is easier and more economical to perform and givesmore accurate control of wall passage shapes, and spacing.

The integral sheet metal tubing useful with this invention may befabricated from strip made by the methods disclosed in U.S. Pat. No.2,690,002, granted to Grenell on Sept. 28, 1954, assigned to theassignee of the instant invention.

Referring now to FIG. 1A, a pattern of weld inhibiting or stop-weldmaterial 1 corresponding to a wall passage 2 of the tube 3 as shown inFIG. 3 is applied to a clean major surface 4 of a strip of metal 5. Asecond strip of metal 6 having a cleaned surface is superimposed on thesurface 4 of the first strip 5, so that the cleaned surfaces are incontact, and the two strips are secured together to prevent relativemotion therebetween. Thereafter, the two superimposed strips 5 and 6 arepressure welded together by rolling so that as shown in FIG. 1B theadjacent areas 7 of the strips 5 and 6 which are not separated by thestop-weld pattern 1 become bonded together. The rolling of the strips 5and 6 results in reducing the thickness of the two superimposed strips 5and 6 and in elongating the resultant blank 8 in the direction ofrolling while the width of the resultant blank 8 remains substantiallythe same as the initial width of the strips 5 and 6. Following therolling operation the blank 8 is usually softened, as by annealing, tomake it more ductile, and if desired, it may be further rolled to thefinal gage desired and again softened as by annealing. The presence ofstop-weld pattern 1 results in the retention of unwelded portions 9extending internally within the blank 8 and sandwiched between its outermajor surfaces 10 and 11. After softening, the blank 8, is formed into atube 3 as shown in FIG. 2. The blank 8 is formed into the tube 3 byconventional means such as rolls or dies. This forming process resultsin a longitudinally extending seam 12 in the tube wall 13. This seam 12results from the butting together of the major edges 14, of the blank 8.

This seam I2 is then joined, preferably by high frequency welding suchas exemplified by the processes of U.S. Pat. Nos. 3,037,105, 2,794,108,and 2,818,488, granted May 29, 1962, May 28, 1957, and Dec. 31, 1957respectively.

The unwelded area 9 of FIG. 2 is then inflated by conventionaltechniques. For example, an inflation needle can be inserted at a freeend F of the stop-weld pattern pattern 1 and a fluid under pressureapplied by the needle to inflate the wall passage 2 as shown in FIG. 3in conformity with the stop-weld pattern 1.

The resultant tube 3 having the wall passage 2 so inflated is shown inFIG. 3 in a cutaway view. It is evident that the wall passage 2configuration may be varied as desired by merely changing the shape ofthe stop-weld pattern 1. FIGS. 4A, B and C illustrate a variety ofpatterns exemplary of those which could be used in accordance with thisinvention. It should be evident that any desired pattern could be formedand used in accordance with the instant invention.

FIG. 4A shows a blank A in accordance with this invention having astop-weld pattern 15 with a generally transverse serpentineconfiguration. The pattern comprises a plurality of passes, 16,connected by a plurality of bend portions 17 with the passes, 16,oriented substantially transverse to the longitudinal direction of theblank A and therefore the longitudinal axis of the resultant tube. Thispattern provides a tube as shown in FIG. 2 and an inflated tube as shownin FIG. 3. This form of pattern provides for termination of the wallpassage, 3, at opposing ends E of the tube 3. A tube 3 formed from theblank A of FIG. 4A has a wall passage'2 having improved heat exchangeefficiency due to the turbulence produced by the plurality of bends, 17,in the serpentine configuration.

A tube as in FIG. 3 formed from the blank A of FIG. 4A has a particularapplication in a countercurrent type heat exchanger wherein the heatexchange fluid flowing through the tube 3 flows in an opposite directionto the fluid flowing in the wall passage 2.

FIG. 4B shows a blank B in accordance with this invention having a stopweld pattern 18 with a generally longitudinal serpentine configuration.The pattern 18 comprises a plurality of passes 19 connected by aplurality of bend portions 20 with the passes 19 oriented substantiallyto the longitudinal direction of the strip and the longitudinal axis ofthe resultant tube. This pattern 18 provides an inflated tube 21 asshown in FIG. 5. The pattern 18 of FIG. 4B provides for termination ofthe wall passage at either the same or opposing ends E of the tube 21. Atube 21. as shown in FIG. 5 has a wall passage 22 having low restrictionto fluid flow because of the large relative length of the passes 23 andthe small number of bends 24.

A tube 21 as in FIG. 5 formed from the blank B of FIG. 4B has particularapplication in situations where it is desirable to heat or cool the tube21 uniformly from one end to the other. Such an application might be forexample the heating of a tube to improve the flow of a viscous fluidsuch as crude oil.

FIG. 4C shows a blank C in accordance with this invention having a dualstop weld pattern 25 with U- shaped configurations. The patterncomprises two U- shaped patterns 26 and 27 oriented with the legssubstantially parallel to the longitudinal direction of the blank C andthe longitudinal axis of the resultant tube 28. This pattern 25 providesan inflated tube 28 as shown in FIG. 6. The pattern 25 of FIG. 4Cprovides for termination of the wall passages 29 at the same end E ofthe tube 28. This type of termination simplifies the plumbingarrangements required for connection to the wall passages 29. A tube 28formed from the blank C of FIG. 4C is adapted for use in situationswhere it is necessary to flow more than one fluid through wall passages29.

A tube 28 as in FIG. 6 formed from the blank C of FIG. 4C has particularapplication in situations where it is desirable to heat or cool morethan one fluid through the use of another fluid while maintainingseparation between the fluids to be heated or cooled. A tube 28 as inFIG. 6 formed from the blank C of FIG. 4C also has the property that atemperature gradient exists from one side of the tube to the other. FIG.6 also shows the application of external fins, 35, which will bediscussed later.

In a practical situation, the inflation pressure required to causepermanent distension of the passage 2 wall will commonly fall within therange of 500 to 4,000 psi, depending upon the metal, the degree of coldwork in the metal, and the thickness of the passage walls. Thedifference in pressure from one side of the wall passage 2 to the otherside, or differential pressure, acts to set up a state of stress withinthe wall passage wall. Permanent distension will occur only when thestate of stress in the wall passage wall exceeds the yield stress forthe metal alloy/condition which comprises the wall passage wall.

In the tube 3 of FIG. 3 the wall passage has been inflated withoutconstraint and the resultant wall passage 2 protrudes interiorly andexteriorly of the tube wall 13.

In order to control or eliminate the degree of protrusion of the wallpassage, it is necessary to control the pressure differential across thepassage wall. If this pressure differential is reduced to below thatwhich will cause yielding of the passage wall, no protrusion of theinflated passage will occur on that side of the tube wall where thepressure differentials is reduced.

The differential pressure which produces the state of stress equal tothe yield stress of the passage wall, is denoted by the letter X. Inorder to eliminate protrusion of the inflated passage from one side ofthe tube, it is necessary to apply a counter balancing fluid pressure,denoted by the letter Y, to the inflation pressure, denoted by theletter Z, on that side of the tube such that the absolute value of Yminus Z is less than or equal to X.

If the above equation is not obeyed because the inflation pressure istoo great, protrusion will occur. In the preferred embodiment, theabsolute value of the differential pressure used falls in the range of100 to 500 psi.

A distension of the passage which causes the protrusion from the tubewall occurs only when differential pressure across the tube wallproduces a stress within the tube wall which exceeds the yield point ofthe metal which comprises the tube wall. Control of this differentialpressure can be used to control the protrusion of the wall passage andeven to eliminate such protrusion from the inner or outer surface of thetube.

For certain heat exchange applications, it may be desirable to have theinner or outer of the tube essentially smooth. For example a smoothinner surface is conductive to higher fluid flow rates than an irregularor rough inner surface. For this reason the instant invention alsoincludes a method and apparatus for inflating the wall passages so as toprovide either a smooth inner or outer tube surface.

Referring to FIG. 5, there is shown a tube 21 having a smooth outersurface formed in accordance with this invention. The tube is formedfrom a blank as shown in FIG. 48. All distension of the wall surface hastaken place interiorly of the tube so that the wall passage 22 protrudesfrom the inner surface 33 of the tube 21 and does not protrude from theouter surface 32 of the tube.

A tube 21 as in FIG. 5 is by virtue of its smooth outer surface 32uniquely adapted to have heat exchange enhancement means affixed to itsouter surface 32. For example a fin or tube configuration ofconventional design can be provided as shown in FIG. 6 by affixing finstock 35 to the smooth outer surface of the tube 28.

A typical application for such a heat exchange device is in the internalcombustion engine wherein it is desirable to equilibrate the temperatureof the cooling media and the engine oil while at the same time rejectingheat to the atmosphere. In use, the cooling media might be caused toflow through the tube 28 and the engine oil caused to flow through thewall passage 29. In use the cooling media and engine oil would approachthe same temperature and heat would be rejected to the atmosphere.

The method and apparatus for forming the tube 28 in accordance with FIG.5 will be described with reference to FIG. 7.

Pump 37 applies fluid pressure through nozzle 38 to inflate the unweldedareas of the tube 44 as previously described. The tube is housed in asealed chamber 41. The ends of the tube are sealed by plugs 40 and 40with the interior of the tube containing a fluid at a low pressure. Thechamber 41 is pressurized by pump 42 through tube 43. The pressureapplied by pump 42 is greater than the pressure applied by pump 37. Byproper control of the relative values of the three pressures; thepressure within the tube 44, the pressure within the wall passage 45 andthe pressure within the sealed chamber 41, the inflation of the wallpassage will be limited to the interior of the tube.

In a practical situation, the pressure required to cause the inflationof the wall passage 45 will commonly fall between 500 and 4000 psi,depending upon the metal and the thickness of the passage walls 39. Inorder to eliminate protrusion, it is necessary only that the pressure onthe side of the tube from which the protrusion is to be eliminatedexceed the pressure within the wall passage. In the preferred.embodiment, the differential pressure falls in the range of to 500 psi.

FIG. 8 shows a tube 49 with a smooth inner surface 46 formed inaccordance with this invention. The tube is formed from a blank of FIG.4C. All distension of the wall passage 47 has taken place exteriorly ofthe tube 49. It is shown that the wall passage 47 protrudes from theouter surface 48 of the tube and does not protrude on the inner surface46.

The tube 49 of FIG. 8 is by virtue of its smooth inner surface 46uniquely adapted to have heat exchange enhancing means attached to itsinner surface 46. For example, a series of essentially longitudinalinterior fins might easily be applied. This embodiment is shown in FIG.9. Such interior fins 50 would serve to increase the heat transfer fromthe fluid flowing within the tube wall 51 and passages within the wall52. Such fins 59 might be applied to the blank C of FIG. 4C prior to theformation of the tube 51 or might be applied to blank 6 of FIG. 4Cduring the tube forming operation. Such interior fins 50 would serve todecrease the required length of tube for a specific heat exchangeapplication.

The method and apparatus for forming the tube 51 in accordance with theembodiment shown in FIG. 8 will be described with reference to FIG. 10.Fluid pressure is applied by pump 52 through nozzle 54 inserted in thestop weld pattern 25 to cause inflation of the wall passage 61.Simultaneously, fluid pressure is applied by pump 55 through tube 56 andseal 57 to the interior of the tube 58. Seal 57 and plug 53 serve toseal the interior 58 of the tube. The pressure applied to the pump 55exceeds the pressure applied by pump 52 and serves to restrict theexpansion of the wall passage 25 solely to the exterior of the tube 59.The comments made during the discussion of FIG. 7 with regard to thedifferential pressure limits also apply to this apparatus.

In certain situations, it may be desirable to restrict heat transfer tobe solely between the fluid flowing within the tube and the fluidflowing within the wall passage or passages. In this situation, it maybe desirable to apply a layer of thermal insulation 60 to the exteriorwall of the tube as shown in FIG. 11. Such-insulation 60 may be of anyconventional type as known in the art; however, it is preferred to use apolymeric foam type insulation and even more preferred to use a rigidpolyurethane foam type insulation which will add strength and stiffnessto the resulting heat exchange structure.

This invention may be embodied in other forms or carried out in otherways without departing from the spirit or essential characteristicsthereof. The present embodiment is therefore to be considered as in allrespects illustrative and not restrictive, the scope of the inventionbeing indicated by the appended claims, and all changes which comewithin the meaning and range of equivalency are intended to be embracedtherein.

I claim:

1. A method for fabricating a sheet metal heat exchanger of tubularconfiguration for use with two or more fluids, wherein a first fluidflows through the tube, at least one fluid flows through at least onepassage in the wall of tube, said at least one said passage having alength at least 30 percent greater than the length of the tube, themethod comprising:

A. providing two metal strips, each of said strips having two majoredges and two major surfaces;

B. providing at least one continuous pattern of stop weld material onone of the major surfaces of one of said strips, said at least onepattern of stop weld material having a length of at least 30 percentgreater than the length of the strips;

C. positioning said strips so that their major surfaces are insuperposition and that said stop weld pattern lies between the strips;

D. joining the adjacent major surfaces of said strips not separated bystop weld, by pressure welding, to form a welded blank;

E. forming said welded blank into tubing by joining the major edges ofthe welded strip by a high frequency welding process; and

F. inflating said at least one passage by the application of sufficientfluid pressure to cause permanent distension.

2. A method as in claim 1 wherein a fluid pressure greater than theinflation pressure is applied to the inside of the tube during inflationso that the inflated passages do not protrude onto the inner surface ofthe tube.

' 3. A method as in claim 1 wherein a fluid pressure greater than theinflation pressure is applied to the exterior of the tube duringinflation so that the inflated passages do not project out from theouter surface of the tube.

4. A method for fabricating a sheet metal heat exchanger of tubularconfiguration for use with three or more fluids, wherein a first fluidflows through the tube, at least one fluid flows through at least onepassage in the wall of the tube, at least one said passage having alength at least 30% greater than the length of the tube and a furtherfluid contacts the exterior of the tube, the method comprising:

A. providing two metal strips, each of said strips having two majoredges and two major surfaces;

B. providing at least one continuous pattern of stop weld material onone of the major surfaces of one of said strips, said at least onepattern of stop weld material having a length of at least 30% greaterthan the length of the strips;

C. positioning said strips so that their major surfaces are insuperposition and that said stop weld pattern lies between the strips;

D. joining the adjacent major surfaces of said strips not separated bystop weld, by pressure welding to form a welded blank;

E. forming said welded blank into tubing by joining the major edges ofthe welded strip by a high frequency welding process; and

F. inflating said passage or passages by the application of sufficientpressure to cause permanent distension.

5. A method as in claim 4 wherein a layer of thermal insulation isapplied to the exterior of the tube after inflation.

6. A method as in claim 2 wherein a plurality of fins are applied to theinterior of the tube.

7. A method as in claim 4 wherein a fluid pressure greater than theinflation pressure is applied to the inside of the tube during inflationso that the inflated passages do not protrude onto the inner surface ofthe tube.

8. A method as in claim 4 wherein a fluid pressure greater than theinflation pressure is applied to the exterior of the tube duringinflation so that the inflated passage does not project out from theouter surface of the tube.

9. A method as in claim 8 wherein a plurality of fins are attached tothe exterior of the tube.

10. A method as in claim 7 wherein a plurality of fins are attached tothe interior of the tube.

1. A method for fabricating a sheet metal heat exchanger of tubularconfiguration for use with two or more fluids, wherein a first fluidflows through the tube, at least one fluid flows through at least onepassage in the wall of tube, said at least one said passage having alength at least 30 percent greater than the length of the tube, themethod comprising: A. providing two metal strips, each of said stripshaving two major edges and two major surfaces; B. providing at least onecontinuous pattern of stop weld material on one of the major surfaces ofone of said strips, said at least one pattern of stop weld materialhaving a length of at least 30 percent greater than the length of thestrips; C. positioning said strips so that their major surfaces are insuperposition and that said stop weld pattern lies between the strips;D. joining the adjacent major surfaces of said strips not separated bystop weld, by pressure welding, to form a welded blank; E. forming saidwelded blank into tubing by joining the major edges of the welded stripby a high frequency welding process; and F. inflating said at least onepassage by the application of sufficient fluid pressure to causepermanent distension.
 2. A method as in claim 1 wherein a fluid pressuregreater than the inflation pressure is applied to the inside of the tubeduring inflation so that the inflated passages do not protrude onto theinner surface of the tube.
 3. A method as in claim 1 wherein a fluidpressure greater than the inflation pressure is applied to the exteriorof the tube during inflation so that the inflated passages do notproject out from the outer surface of the tube.
 4. A method forfabricating a sheet metal heat exchanger of tubulAr configuration foruse with three or more fluids, wherein a first fluid flows through thetube, at least one fluid flows through at least one passage in the wallof the tube, at least one said passage having a length at least 30%greater than the length of the tube and a further fluid contacts theexterior of the tube, the method comprising: A. providing two metalstrips, each of said strips having two major edges and two majorsurfaces; B. providing at least one continuous pattern of stop weldmaterial on one of the major surfaces of one of said strips, said atleast one pattern of stop weld material having a length of at least 30%greater than the length of the strips; C. positioning said strips sothat their major surfaces are in superposition and that said stop weldpattern lies between the strips; D. joining the adjacent major surfacesof said strips not separated by stop weld, by pressure welding to form awelded blank; E. forming said welded blank into tubing by joining themajor edges of the welded strip by a high frequency welding process; andF. inflating said passage or passages by the application of sufficientpressure to cause permanent distension.
 5. A method as in claim 4wherein a layer of thermal insulation is applied to the exterior of thetube after inflation.
 6. A method as in claim 2 wherein a plurality offins are applied to the interior of the tube.
 7. A method as in claim 4wherein a fluid pressure greater than the inflation pressure is appliedto the inside of the tube during inflation so that the inflated passagesdo not protrude onto the inner surface of the tube.
 8. A method as inclaim 4 wherein a fluid pressure greater than the inflation pressure isapplied to the exterior of the tube during inflation so that theinflated passage does not project out from the outer surface of thetube.
 9. A method as in claim 8 wherein a plurality of fins are attachedto the exterior of the tube.
 10. A method as in claim 7 wherein aplurality of fins are attached to the interior of the tube.